Analog television broadcasts are becoming changed to digital television broadcasts. So far, digital satellite broadcast services using CS (Communication Satellites) have been started. In addition, digital satellite broadcast services using BS (Broadcasting Satellites) are being prepared. Moreover, digital television broadcasts using ground waves are scheduled to be started.
In digital television broadcasts, since the frequency efficiency is improved, more channels can be assigned than analog television broadcasts. In addition, HDTV (High Definition Television) broadcasts can be easily performed. Moreover, in digital television broadcasts, various services such as bi-directional service, data delivery service, and video-on-demand that are not available in conventional analog television broadcasts can be accomplished.
A television receiver that receives such a digital television broadcast is conventionally structured as shown in FIG. 1.
In FIG. 1, a received signal is supplied from an input terminal 101 to a tuner circuit 102. In the case of a CS digital broadcast, a signal of 12 GHz band is received by a parabola antenna (not shown). The received signal is converted into a signal of 1 GHz band by a low noise converter disposed in the parabola antenna. The converted signal is supplied to the tuner circuit 102. The tuner circuit 102 selects a carrier frequency signal of a desired channel from the received signal and performs a demodulating process and an error correcting process for the selected signal. As a result, the tuner circuit 102 decodes the selected signal to a transport stream composed of video packets and audio packets.
An output of the tuner circuit 102 is supplied to a demultiplexer 103. The demultiplexer 103 separates the transport stream into video packets and audio packets.
The video packets are supplied to a video decoder 104. The audio packets are supplied to an audio decoder 105. The video decoder 104 performs a decompressing process for the video packets corresponding to for example the MPEG 2 (Moving Picture Experts Group) system so as to decode the video packets to video data. In addition, the audio decoder 105 performs a decompressing process for the audio packets corresponding to the MPEG system so as to decode the audio packets to audio data.
The video data decoded by the video decoder 104 is supplied to a graphics processing circuit 106. The graphics processing circuit 106 performs a picture process. An output of the graphics processing circuit 106 is output from an output terminal 107. An output of the audio decoder 105 is output from an output terminal 108.
The tuner circuit 102, the demultiplexer 103, the video decoder 104, the audio decoder 105, and the graphics processing circuit 106 are controlled by an MPU (Micro Processor Unit) 111. A bus 110 extends from the MPU 111. The tuner circuit 102, the demultiplexer 103, the video decoder 104, the audio decoder 105, and the graphics processing circuit 106 are connected to the bus 110.
In addition, a modem 112 and for example an IEEE (Institute of Electrical and Electronics Engineers) 1394 interface 113 are connected to the bus 110. The modem 112 is used to perform a charging process. The IEEE 1394 interface 113 exchanges a stream with an external device.
As was described above, in a conventional receiver for a digital television broadcast, the entire receiver is controlled by an MPU. The MPU centrally controls each portion of hardware using commands thereof in consideration of precise timing levels thereof.
However, in that method of which the MPU centrally controls the entire device in consideration of each portion of the hardware, since the design work should be performed for each device, if the design of the device is changed, software should be largely rewritten and hardware should be largely changed. Thus, the developing efficiency of such a method is low. In addition, since parts cannot be used in common or structured as modules, the cost of the device may rise. In addition, the size of the device may become large. Moreover, digital television broadcasts provide various types of services. Thus, in the method of which the MPU centrally manages the entire device, it is difficult to deal with new services.
Thus, functions necessary for a television receiver may be structured as blocks and connected through a common bus. For conventional television receivers, a standardized controlling bus has been proposed.
However, the conventional controlling bus is used to exchange control data among the MPU and the individual blocks. Thus, streams of video data and audio data are not sent to the bus. In a digital television broadcast, since streams of video data and audio data should be processed, the conventional bus that exchanges only control data cannot be used.
Although a bus for control data and another bus for streams of video data and audio data may be separately disposed, streams and control data should be synchronized. To do that, a timing signal is required. When the timing signal is sent, the buses depend on hardware. Thus, a general-purpose designing method cannot be used.
On the other hand, in personal computers, there are standardized buses such as PCI (Peripheral Component Interconnect) and ISA (Industry Standard Architecture). Like personal computers, in television receivers for digital television broadcasts, it is likely that a standardized bus is required.
However, in personal computers, when hardware for a new function is connected to a bus, software of a driver for the hardware should be installed. Thus, the user should perform the installing operation for the software.
When a digital television broadcast is processed, streams of video data and audio data that are transferred at high speed should be processed. However, when a personal computer handles such streams, a high speed CPU and a large capacity memory are required.
Therefore, an object of the present invention is to provide a digital signal processing apparatus and a receiving method that allow the developing efficiency to be improved and the design to be easily changed.
Another object of the present invention is to provide a digital signal processing apparatus and a method that allow a new service and a change of a broadcasting system to be easily handled.